In general, gelatin is widely used since it has many advantages as a base material of a capsule coating, such as reversible sol-gel transformation by a temperature change, normal gelation temperature, excellent film formability, high mechanical strength of formed film, solubility in a body, high nutritional value of itself, and absorbability in a body.
Incidentally, when a capsule for medicament quickly dissolves in acidic secretions in the stomach, the medicament is released in the stomach, which is not preferable in terms of side effects thereof, persistence of the drug action, and the like.
From these viewpoints, various enteric capsules have conventionally been proposed.
In one example, a surface of a capsule coating is coated with an enteric polymer material, such as zein, shellac, and Eudragit to make a tri-layered structure. However, it is difficult to strictly control the conditions in the coating process, and difference in the coating layer thickness among lots, unevenness in a coating layer of each capsule, or peeling of a coating layer, and the like arise depending on the technical level of the worker, possibly causing variation in the enteric function.
On the other hand, examples of a capsule coating that imparts the enteric property without any coating process include a gelatin-based capsule coating having a low methoxyl pectin incorporated therein as described in PTL 1. However, a low methoxyl pectin is insolubilized in the presence of divalent or monovalent cations. Thus, when the capsule content contains divalent or monovalent cations, it is difficult to control the enteric property and the raw materials to be incorporated in the capsule content are restricted in production of a capsule formulation. In addition, when the content containing divalent or monovalent cations is used for a capsule formulation, the content possibly fails to be absorbed in the body due to the delayed disintegration in the intestines.